Pirbright: SARS-CoV-2 Has Ability to Enter Animal Cells in Lab Setting

Merged cells following co-expression of the SARS-CoV-2 spike glycoprotein and human ACE2 receptors. The spike glycoprotein induces cell-cell fusion after engaging with ACE2, allowing a fluorescent protein to become activated. ( The Pirbright Institute )

Scientists at the Pirbright Institute Laboratory have shown that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus responsible for COVID-19, has the ability to enter some animal cells in vitro using the receptors found in multiple animal species, The Pirbright Institute reports in a release. 

Although the broad host range of SARS-CoV-2 confirms the potential risk of infection to a wide range of companion animals, livestock and wildlife, Dave Pyburn, DVM, chief veterinarian at the National Pork Board, says no studies have been able to infect pigs with SARS-CoV-2 to this point.

According to Pyburn, of the six individual research groups he knows of that are studying the pig’s ability to contract SARS-CoV-2, the virus has not been able to be transmitted to pigs.

The Centers for Disease Control and Prevention (CDC) says the virus that causes COVID-19 spreads from person to person, and there is no evidence at this time to suggest animals play a significant role in spreading the virus, Pyburn adds. 
“Early research has found that pigs are not susceptible to infection by the SARS-CoV-2 virus, which causes COVID-19. The theory here is that the pig’s cells do not have the right receptors for viral attachment and cell entry for the establishment of an infection,” Pyburn explains.

Like other human coronavirus diseases such as severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS), COVID-19 is a zoonotic disease that has jumped from animals to humans, Pirbright reports. 

“Identifying the original animal reservoir for SARS-CoV-2 and intermediate hosts which spread the virus to humans may ultimately help us to understand how, where and when this virus spilled over into humans. This knowledge could be vital in preventing subsequent outbreaks of both related and unrelated viruses,” the release said.

To enter cells, SARS-CoV-2 uses its spike glycoprotein to bind to ACE2 receptors on the surface of cells in various tissues including the lungs, heart and gastrointestinal tract, Pirbright reports. Researchers experimentally infected cells displaying human ACE2 or a panel of related ACE2 receptors from 22 animal species.

The pre-published study demonstrates that the spike glycoprotein uses ACE2 receptors from each species differently, but dog, cat and rabbit receptors were utilized most effectively. Pirbright says this easier entry could potentially correlate with infection being more easily established.

It is critical to point out that SARS-CoV-2 cell entry is just the first step in viral transmission between different animal species. 

“An animal’s susceptibility to infection and its subsequent ability to infect others is reliant on a range of factors such as whether SARS-CoV-2 is able to replicate once inside cells and the animal’s ability to fight off the virus,” Pirbright says. “Interestingly, although bats are suspected to be the original reservoir of SARS-CoV-2, the results show that receptors from three bat species were among those that were least efficiently used by the spike glycoprotein.”

Scientists say this may be caused by adaptations SARS-CoV-2 has made during its zoonotic emergence to effectively bind to human ACE2 receptors.

More detailed investigations and experimental animal challenge studies are needed to ascertain whether livestock and companion animals could be receptive to COVID-19 infection from humans and act as reservoirs for this disease, Pirbright says. 

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